My tub is 330 gallons. My SWG is a bit different, it is part of the tub itself and has a setting from 1-10, I have found that 6 seems to keep it where I want it, although I did an ahh-some purge yesterday so I am curious if it will be able to run a little bit lower as I got quite a bit of gunk out which I am sure was chewing through some chlorine. I have found too, after the kids have friends over (and have the same scenerio as you), that cleaning the filters helps get things back in check as well especially the foaming.
Don't know how true this is but I heard that our built in salt system runs double of the level it's set at. For example, 4 would mean it runs for 8hrs, 6 would be 12hrs and so on. And Boost runs for 24hrs. My tub is 350 gallons and with a setting of 6, it will maintain the fc level.